The invention relates to a continuous method for the preparation of substituted or unsubstituted cyanacetaldehyde acetals by the reaction of alpha-carbon-substituted or unsubstituted beta-alkoxy-acrylonitriles with alcohols in the presence of catalytic amounts of a suitable base at elevated temperature.
According to Am. Chem. Soc. 69 (1974) pages 2657-2660, the treatment of beta-ethoxyacrylonitrile with alcohol in the presence of small amounts of sodium ethoxide leads to the formation of the cyanoacetal by the quantitative addition of the alcohol. Separation of the product, however, is difficult, because the attempt to isolate it by heating with a few drops of concentrated sulfuric acid led to the reformation of the beta-ethoxyacrylonitrile starting substance in the amount of only 40%. According to the inventor's own studies, the reaction is incomplete and the transposition, even on the hundred-gram scale of operation, requires a great amount of time, and in the case of larger quantities the purity of the products is decidedly reduced.
Other methods of preparation, for example by the transposition of bromoacetaldehyde acetal with alkali cyanides or of beta-chloracrylonitrile with sodium alcoholate and alcohols are difficult to practice, the starting substances are difficult to obtain, and the yields achieved are moderate.
These known methods of preparation also can be practiced only discontinuously, the processing of the reaction solutions, such as neutralizations and separation of solids, is difficult and time-consuming, and calls for a great amount of safety measures and environmental safeguards.
The aim to be accomplished was therefore to prepare cyanacetaldehyde acetals by an economical and easily accomplished method, preferably adapted to a continuous industrial procedure. It is also desired to have the reaction go virtually to completion in a reasonably short period of time, to allow production of the product in pure form.